Method of preventing surge in the compressor of a refrigeration system



Jan. 24, 1967 H. LEONARD, JR 3,299,654 METHOD OF PREVENTING SURGE IN THE COMPRESSOR OF A REFRIGERATION SYSTEM Filed Jan. 29, 1965 LOUlS H. LEONARD, JR.

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ATTORNEY.

United States Patent 3,299,654 METHOD OF PREVENTENG SURGE IN THE COM- PRESSOR OF A REFRIGERATION SYSTEM Louis H. Leonard, Jr., Dewitt, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Jan. 29, 1965, Ser. No. 429,036 6 Claims. c1. 62116) This invention relates to gas compression and, more particularly, to a method of effectively preventing compressor surge as in a refrigeration system.

The illustrated embodiment of the invention is directed to effectively preventing surge of a centrifugal compressor in a steam-powered refrigeration system by passing steam through the compressor along with the refrigerant gas as a surge condition is approached. Thus, the compressors stable operating range is increased and it continues in normal operation at a very small cooling capacity. If a centrifugal compressor goes into surge, it ceases to function as a compressor. A violent surge condition, with rapidly changing pressure conditions, causes high intermittent loadings on the compressor bearings and may result in rapid bearing failure. The invention comprehends the use of a surge preventing vapor which has a substantially higher specific volume than the refrigerant and in liquid state is immiscible with refrigerant liquid so that mixed refrigerant and surge preventing fluids may be easily separated from each other and returned for reuse in the system.

It is a primary object of this invention to provide a new and improved method of gas compression and, more particularly, of effectively preventing centrifugal compressor surge as in a refrigeration system and extending the effectiveoperating range of the compressor, for example at low cooling capacity.

Another object is provision of a new and improved method of effectively preventing centrifugal compressor surge in a steam-powered refrigeration system by passing steam through the compressor as the compressor approaches a surge condition. A related object is provision in such a method for separating the refrigerant and surge preventing fluids and returning at least one of the separated fluids for reuse in the system. Other objects of the invention will be readily apparent from the following description:

This invention relates to a method of effectively preventing surge in a system having a compressor for compressing a first gas. The compressor is operated to compress the first gas. A second gas is provided having a relatively high specific volume. The second .gas is passed through the compressor with the first gas as the compressor approaches surge condition. The drawing is a schematic flow diagram of a preferred embodiment of the invention.

The invention is generally applicable for preventing surge in any suitable gas compression system for example, in a steam-powered centrifugal compressor refrigeration system as disclosed in my copending United States patent application S.N. 379,446, filed July 1, 1964, for Refrigeration Apparatus, now abandoned, a continuationin-part application Ser. No. 473,245 having been filed on July 19, 1965 and reference may be had thereto for a more complete discussion of such a system in general.

The invention will be described with reference to the foregoing refrigeration system including a preferred power and surge preventing fluid which is steam, and a preferred refrigerant which is octafluorocyclobutane, commonly referred to as C318 and having a formula C 1 These fluids are particularly preferred because steam has a relatively high specific volume and is relatively immiscible with the refrigerant, and because they are inherent- Patented Jan. 24, 1967 ly highly stable and do not tend to decompose or chemically react With each other or other materials in the system, or cause or promote corrosion or undesirable by-products. Also, this refrigerant is a relatively noncondensible vapor at the temperature and pressure at which the power fluid (steam) condenses as Well as at the usual ambient atmospheric conditions of temperature and pressure. However, other power and surge preventing fluids and gases to be compressed other than refrigerant C318, for example, propane, having the desired chemical and physical properties may be utilized within the scope of this invention.

Referring to the drawing, there is shown a refrigeration system which includes a steam boiler 11 communicating through a steam line 12with the inlet of a turbine 13 of a turbocompressor 14 from which the steam is discharged through a discharge line 15 to a steam condenser 16. From the steam condenser 16 the steam condensate flows through a port 17 into a condensate chamber 18 and is returned to the boiler 11 through a steam condensate return line 19 including a suitable steam condensate pump 20. The turbine 13 drives a centrifugal refrigerant compressor 21 of the turbocompressor 14.

The compressor 21 receives refrigerant gas such as vapor, for example, through a suction line 22 on the low pressure side of the system and passes the compressed gas through the high pressure refrigerant vapor or gas line 23 to a refrigerant condenser 24 on the high pressure side of the system. The condensate flows through a refrigerant condensate line 25 including suitable flow restricting means such as a float valve unit 26, and into a body of liquid refrigerant in a pan 27 elevated above the bottom of a shell 28 of an evaporator or cooler 29. Leaving and returning branches of a chilled water line 30 communicate with a chilled water bundle 31 flooded with refrigerant in the pan 27, for circulating chilled water to a load having a cooling requirement. From the cooler 29, refrigerant gas returns to the compressor through the suction line 22.

Capacity control of the system is effected by passing refrigerant gas at a regulated rate through a line 32 from the refrigerant condenser 24 into the steam condenser 16 to regulate the output of the turbine 13 and thereby the compressor 21 and the system as a whole. A modulating refrigerant valve 33 in the line 32 may be controlled' in any suitable manner as by an actuator responsive to a sensor 34 on the leaving branch of the chilled Water line 30. A constant rate refrigerant purge system withdraws refrigerant vapor or gas from the steam condenser 16 and includes a purge line 35 opening into an upper portion of a steam condensate chamber 18 and connecting into a water driven jet pump 36 from which the mixture of water and refrigerant gas passes through a line 37 into the bottom of the cooler 29 which includes a sump 38 for water.

Impeller water for driving the jet pump 36, and makeup water for the boiler 11 is provided through a water supply line 39 including a water supply pump 40. A make-up water line 41 branches ofl of the water supply line 39 upstream of the jet pump 36 and includes a normally closed shut-off valve 42 which is opened responsive to a low Water level in the condensate chamber 18, as by a float sensor 43 in the chamber.

Refrigerant and steam mixed in the steam condenser 16 is separated as the steam condenses and collects in the condensate chamber 18. The refrigerant vapor passes through the purge system and into the cooler sump 38 and steam condensate returns to the boiler through condensate line 19 as previously described. Refrigerant in the cooler sump 38 boils out of the sump water because heat in the hot refrigerant vapor from the steam condenser 16 and the heat of the water supply pump 40 raises the temperature of the sump water above the boiling temperature of the refrigerant in the cooler. The refrigerant boiled out of the sump water passes about a free left end of the pan 27 and through the suction line 22 back to the compressor 21. Any water passing into the pan 27 from the refrigerant condenser 24 floats atop the boiling refrigerant in the pan and passes to a free end of the chilled water bundle 31 where it collects in a pool and passes through a suitable weir or port (not shown) in the free left end of the pan and into the sump 38 for return to the steam condensate chamber 18 through the make-up water line 41.

Means is provided for effectively preventing compressor surge, as at low cooling capacity of the system when a small volume of refrigerant is passing through the compressor 21. A branch steam line 44 connects the steam supply line 12 and the suction line 22 for passing steam to the compressor inlet. A suitable steam valve 45, preferably of the modulating type, is provided in the branch steam line 44 and is operated responsive to a suitable sensor 46 as on the leaving branch of the chilled water line 30 for opening the valve 45 when the leaving chilled water temperature drops below a predetermined temperature or, alternatively, a sensor (not shown) on the leaving and returning branches of the chilled water line for operating the modulating steam valve 45 responsive to a predetermined small diiference in the entering and leaving chilled water temperatures.

When passed through the compressor in combination with the refrigerant at low cooling capacity operation, a fluid having a very high vapor specific volume, such as steam, causes the compressor 21 to compress enough of the vapor mixture to effectively prevent surge as the cooling capacity of the system is substantially reduced.

The present surge prevention expedient is more effective than a conventional hot gas bypass using the refrigerant gas from the compressor outlet or the condenser to keep the compressor loaded up and out of surge. This is because the mixture of water vapor and refrigerant vapor or gas weighs much less per cubic foot than pure refrigerant vapor and accordingly takes less horsepower per ton to compress, thus, partial load operating costs are reduced.

While a preferred embodiment of the invention has been described and illustrated, it will be understood that the invention is not limited thereto but may be otherwise embodied within the scope of the following claims.

I claim:

1. A method of effectively preventing surge in a system having a centrifugal compressor for compressing a first gas, comprising the steps of operating the compressor to compress the first gas, providing a second 4 gas having a relatively high specific volume, sensing approach of the compressor to surge condition and responsive thereto passing said second gas through the compressor with the first gas thereby effectively preventing surge.

2. The method of claim 1 wherein the second gas is steam.

3. The method of claim 1 wherein the second gas is steam and said first gas is refrigerant C318.

4. A method of effectively preventing surge in a system having a steam driven centrifugal compressor for compressing a first fluid immiscible with water, comprising the steps of operating the compressor to pass first fluid gas through the system, sensing approach of the compressor to surge condition and responsive thereto passing steam along with the first fluid gas through the compressor, whereby the total volume of compressed gas is substantially larger than the volume of first fluid gas compressed, thereby loading the compressor and effectively preventing surge.

5. The method of claim 4 and the additional steps of, separating the fluids after they are compressed, and returning at least one of the separated fluids for reuse in the system.

6. A method of effectively preventing surge in a refrigeration system having a steam driven centrifugal refrigerant compressor for compressing refrigerant C318 circulated through the system to provide cooling, comprising the steps of operating the compressor to compress refrigerant gas and pass the gas from the low side to the high side of the system, automatically sensing approach of the compressor to a surge condition and responsive thereto mixing steam with the refrigerant gas entering the compressor, whereby the total volume of gas compressed is substantially larger than the volume of refrigerant gas compressed, thereby loading the compressor and effectively preventing compressor surge while the cooling capacity of the system is reduced, separating the mixed fluids, and returning the separated fluids for reuse in the system.

References Cited by the Examiner UNITED STATES PATENTS 2,682,756 7/1954 Clark et a1 62502 X 2,794,328 6/1957 Herrick 62502 X 2,951,350 9/1960 Etherington et al. 62502 X 2,983,111 5/1961 Miner et al 621 15 3,172,270 3/1965 Mirante 62-116 LLOYD L. KING, Primary Examiner. 

1. A METHOD OF EFFECTIVELY PREVENTING SURGE IN A SYSTEM HAVING A CENTRIFUGAL COMPRESSOR FOR COMPRESSING A FIRST GAS, COMPRISING THE STEPS OF OPERATING THE COMPRESSOR TO COMPRESS THE FIRST GAS, PROVIDING A SECOND GAS HAVING A RELATIVELY HIGH SPECIFIC VOLUME, SENSING APPROACH OF THE COMPRESSOR TO SURGE CONDITION AND RESPON- 